1. Field of the Invention
The present invention relates to a hard disk drive equipped with a noise canceler to prevent noise, introduced by a driving current, from being supplied to a voice coil motor which moves a magnetic head.
2. Description of the Related Art
A voice coil motor (hereinafter referred to as a VCM) is generally used on a hard disk drive as a driving source for moving a carriage which is supporting a magnetic head. The carriage is driven by a driving current supplied to the VCM. When the carriage is driven, the magnetic head supported on the end of the carriage moves in the radial direction of a recording medium (disk) for data recording or reproducing.
An existing VCM driving system is composed of a printed circuit board (hereinafter referred to as a PCB), a flexible printed cable (hereinafter referred to as a FPC) and a VCM.
There are provided a resistor for adjusting a driving current being supplied to the VCM and a motor driver comprising a plurality of transistors as switching devices on the PCB. In addition, the PCB is provided with a lowpass filter comprising a resistor and a capacitor. The FPC is provided with a VCM current line for connecting the motor driver on the PCB to the VCM. Furthermore, the FPC is provided with various signal lines such as data lines for data transfer between the magnetic head and a read/write circuit provided on the PCB.
When driving the VCM in the construction as described above, in order to get the magnetic head to seek in the positive direction (for instance, in the inner peripheral direction of a disk) or the negative direction (for instance, in the outer peripheral direction of a disk) it is necessary to flow a driving current being supplied to the VCM in a first direction or a second direction which is opposite to the first direction. For this purpose, a switching circuit has been composed by a plurality of transistors as described above.
When driving the VCM, the driving current is applied in the first direction in order to move the magnetic head in the positive direction by turning some of the transistors on selectively and by turning the remaining transistors off. On the contrary, the driving current is applied in the second direction in order to move the magnetic head in the negative direction by turning on the transistors which were turned off when moving the magnetic head in the positive direction and by turning off those transistors which were turned on at the time.
As described above, on the VCM driving system, the magnetic head is moved in the positive or negative direction by applying the driving current to the VCM by turning on/off a plurality of transistors comprising a switching circuit provided in the PCB.
Here, there is such a problem that a switching noise is generated when the transistors are selectively turned on/off. For the purpose of cancelling this switching noise, lowpass filters comprising resistors and capacitors have been provided in the PCB.
In an existing VCM driving system, however, these lowpass filters were simply incorporated in parallel with the VCM so far and therefore, there was such a defect that a noise which couldn't be cancelled, that is, a leakage component (a high frequency component) of the noise flows into the VCM current line in the FPC.
Up to now, the VCM current line was provided using a separate cable different from a data line to the magnetic head. However, according to demands for downsizing a hard disk drive in recent years, the VCM current line has come to be provided on the FPC on which a data line is also provided. So, there were such problems-that if an uncancelled noise was on the VCM current line, the data line was also adversely affected, resulting in drop of data recording/reproducing accuracy and the like.